Hänninen Mikko M, Mota Antonio J, Sillanpää Reijo, Dey Sourav, Velmurugan Gunasekaran, Rajaraman Gopalan, Colacio Enrique
Department of Chemistry , University of Jyväskylä , P.O. Box 35, FIN-40014 Jyväskylä , Finland.
Departamento de Química Inorgánica, Facultad de Ciencias , Universidad de Granada , Avda. de Fuentenueva s/n , 18071 Granada , Spain.
Inorg Chem. 2018 Apr 2;57(7):3683-3698. doi: 10.1021/acs.inorgchem.7b02917. Epub 2018 Mar 22.
A family of MnLn strictly dinuclear complexes of general formula [Mn(μ-L)(μ-OMe)(NO)Ln(NO)(MeOH)] (Ln = Gd, Dy, Er, Ho) has been assembled in a one pot synthesis from a polydentate, multipocket aminobis(phenol)ligand [6,6'-{(2-(1-morpholyl)ethylazanediyl)bis(methylene)}bis(2-methoxy-4-methylphenol)], Mn(NO)·4HO, Ln(NO)· nHO, and NEt in MeOH. These compounds represent the first examples of fully structurally and magnetically characterized dinuclear MnLn complexes. Single X-ray diffraction studies reveal that all complexes are isostructural, consisting of neutral dinuclear molecules where the Mn and Ln metal ions, which exhibit distorted octahedral MnNO and distorted LnO coordination spheres, are linked by phenoxide/methoxide double bridging groups. Static magnetic studies show that the MnGd derivative exhibits a weak antiferromagnetic interaction between the metal ions, with a negative axial zero-field splitting D parameter. The MnGd complex shows a notable magnetocaloric effect with magnetic entropy change at 5 T and 3 K of -Δ S = 16.8 J kg K. Theoretical studies were performed to support the sign and magnitude of the magnetic anisotropy of the Mn ion ( ab initio), to predict the value and nature of J, to disclose the mechanism of magnetic coupling, and to establish magneto-structural correlations (DFT calculations). The results of these calculations are corroborated by quantum theory of atoms in molecule analysis (QTAIM). Finally, Mn-Dy and Mn-Er complexes show field-induced slow relaxation of the magnetization but without reaching a maximum above 2 K in the out-of-phase ac susceptibility. Ab initio calculations were also performed on Mn-Dy/Ho systems to unravel the origin behind the weak SMM characteristics of the molecules possessing two strongly anisotropic ions. The mechanism of magnetic relaxation was developed, revealing a large QTM/tunnel splitting at the single-ion level. Furthermore, the anisotropy axes of the Mn and Ln ions were calculated to be noncollinear, leading to reduction of the overall anisotropy in the molecules. Hence, the herein reported complexes demonstrate that a combination of two anisotropic metal ions does not guarantee SMM behavior.
通过在甲醇中，由多齿、多口袋氨基双（苯酚）配体[6,6'-{(2-(1-吗啉基)乙基氮杂二亚基)双(亚甲基)}双(2-甲氧基-4-甲基苯酚)]、Mn(NO)·4H₂O、Ln(NO)·nH₂O和NEt进行一锅法合成，组装得到了通式为[Mn(μ-L)(μ-OMe)(NO)Ln(NO)(MeOH)]（Ln = Gd、Dy、Er、Ho）的MnLn严格双核配合物家族。这些化合物代表了首批在结构和磁性方面得到充分表征的双核MnLn配合物实例。单晶X射线衍射研究表明，所有配合物均为同构结构，由中性双核分子组成，其中呈现扭曲八面体MnNO和扭曲LnO配位球的Mn和Ln金属离子通过酚盐/甲氧基双桥连基团相连。静态磁性研究表明，MnGd衍生物在金属离子之间表现出弱反铁磁相互作用，轴向零场分裂D参数为负。MnGd配合物在5 T和3 K时具有显著的磁热效应，磁熵变为-ΔS = 16.8 J kg⁻¹ K⁻¹。进行了理论研究以支持Mn离子磁各向异性的符号和大小（从头算），预测J的值和性质，揭示磁耦合机制，并建立磁结构相关性（密度泛函理论计算）。这些计算结果通过分子中的原子量子理论（QTAIM）得到了证实。最后，Mn-Dy和Mn-Er配合物表现出磁场诱导的磁化缓慢弛豫，但在异相交流磁化率中在2 K以上未达到最大值。还对Mn-Dy/Ho体系进行了从头算，以揭示具有两个强各向异性离子的分子的弱单分子磁体特性背后的起源。发展了磁弛豫机制，揭示了单离子水平上的大量子隧穿/隧穿分裂。此外，计算得出Mn和Ln离子的各向异性轴不共线，导致分子中整体各向异性降低。因此，本文报道的配合物表明，两种各向异性金属离子的组合并不能保证单分子磁体行为。
